1. Field of the Invention
The present invention relates to a method of and an apparatus for controlling piezoelectric vibration, and more particularly to a method of controlling vibration of a piezoelectric vibrator used for a parts feeder or the like to feed various types of parts by vibration as well as to a system for the same.
2. Description of the Prior Art
The conventional type of vibration control for a parts feeder having a bowl for accommodating therein parts and discharging out each of the parts by exerting vibration to the bowl, for example, as disclosed in published Japanese Patent Application, KOKAI (Early Publication) No. 57-27808, is effected by detecting the vibration of the bowl by a photoelectric transducer, feeding back an amplitude of the bowl obtained thereby to an amplitude controlling circuit, controlling a current fed to an electromagnet for driving the bowl, and driving the bowl at a constant amplitude at any time.
In another system, as disclosed in U.S. Pat. No. 5,372,237 issued Dec. 13, 1994 to Susumu Yagi, parts accommodated in a bowl are fed from a parts discharging section to a shoot due to vibration of the bowl, and when each part slides down the shoot to be fed to an assembling machine, the part passing through the shoot is detected by a photoelectric sensing element to control the parts feeding rate.
In a case of the method based on the conventional technology, the amount of parts supplied from the parts feeder varies according to changes in external environments such as a voltage or temperature, and for this reason it is quite hard to feed parts with stability. To control the parts feeding rate, the parts feeder is provided with such a sensor as a photoelectric transducer for detecting mechanical vibration or movement and converting it to an electric signal for feedback control. Accordingly, a control system becomes complicated with size of the apparatus increased, and also the cost becomes high.